1. Field of Invention
The present invention relates to a video processing apparatus and method, and more particularly, to a video processing apparatus and method capable of processing access rights to a video that only an authorized user can view, with a high degree of reliability.
2. Description of the Related Art
A video processing apparatus such as a set-top box, a television and so on, receives video signals containing a video from broadcasting stations as over-the-air TV broadcasting signals, cable TV broadcasting signals and the like, or receives video signals from various video apparatuses such as a video cassette recorder (VCR) and a digital versatile disk (DVD) player. The apparatus conducts the appropriate video processing on the received or input video signals, and then outputs the processed video. Particularly, a video processing apparatus such as a cable set-top box and a cable-ready television can receive and properly process cable TV broadcast signals.
A cable TV system that broadcasts cable TV signals is configured with a multiple services operator (MSO) and a cable television headend (hereafter, referred to as a headend). The MSO provides diverse cable TV services including multimedia services for video and audio, and data services for data information. The headend receives the cable TV signals from the MSO, processes, and distributes the received signals. While communicating data with the MSO over a network, the headend receives incoming service signals and forwards them to a cable network which has a local cable infrastructure.
A cable set-top box or a cable-ready TV receives the cable TV service signals from the headend over the cable network and properly processes the received signals so as to provide the services to a user. A TV connected to the cable set-top box or the cable-ready TV outputs video or audio, or provides data services to the user based on the processed signals.
In such cable TV broadcasting system, certain services among the provided services can be accessed only by an authorized user. Such access control is called conditional access (CA). One of the CA implementation schemes is to operate the cable set-top box or the cable-ready TV in conjunction with a CA processing device called a Point of Deployment (POD) module. For example, according to the OPENCABLE™ specification, a CABLECARD™ can be mounted in the cable set-top box or the cable-ready TV as the POD module to process the CA. The POD module selectively decrypts or descrambles encrypted or scrambled video signals which have been received at the cable set-top box or the cable-ready TV. Hereafter, the POD is referred to as a “cable card”, and the cable set-top box or the cable-ready TV is referred to as a “host” in relation with the cable card.
FIG. 1 depicts CA operations between a conventional host and cable card. When a user selects a scrambled channel at a host, the host sends to the cable card a message ca_info_inq inquiring about information relating to the CA, at operation S1. In response to this message, the cable card sends its held CA-related information ca_info to the host, at operation S2. Since this procedure can be performed in cases when, for example, the cable card is initially mounted to the host, it is called initialization. The information ca_info includes CA_system_ID which is an identifier of the CA system.
Next, the host receives cable TV broadcast signals from the headend and sends a CA program map table CA PMT containing access rights information of the user in relation with the current channel and a message ca_pmt_cmd_id inquiring about the user's access rights to the POD, at operation S3. The access rights information of the user in relation with the current channel may be a CA descriptor, by way of example. The cable card replies to the host with a message ca_pmt_reply indicating the access rights information of the user with respect to the current channel, at operation S4. At this time, the cable card determines whether or not the user is authorized to access the current channel, based on the received CA descriptor. The message ca_pmt_reply indicating whether or not the user is authorized to access the current channel contains information CA_enable indicative of whether the current channel is descrambled. In response to this message, the host sends a message ca_pmt_cmd_id indicating a subsequent action, to the cable card, at operation S5.
However, the host may receive from the headend an improper CA descriptor or a plurality of CA descriptors as the CA descriptor which is the criterion to determine whether the user is authorized to access the current channel. FIG. 2 outlines operations of the conventional host and cable card in this situation.
If the user selects a scrambled channel at the host, at operation S11, the host receives an improper CA descriptor or a plurality of CA descriptors from the headend, at operation S12. The host generates a CA PMT message using the improper CA descriptor or the plurality of CA descriptors at operation S13, and sends the generated CA PMT message to the cable card, at operation S14. Since the transferred CP descriptor is improper or plural in number, the cable card determines that the user is not authorized to access the current channel. Then, at operation S15 the cable card responds to the host with a message indicating the result of the determination. Because it is determined that the user is not authorized for the current channel, the host cannot decode the current channel, and thus displays no video, at operation S16.
As discussed above, in the case where the host sends an improper CA descriptor or plural CA descriptors to the cable card, the related art has the disadvantage that the user cannot view the current channel even though the user is authorized to access the current channel.